Method for polymerizing olefinically unsaturated monomers employing a catalyst composition comprising (a) shock-sensitive organic peroxide and (b) an olefinic unsaturated non-homopolymerizable monomer

ABSTRACT

Organic peroxide compositions suitable for free radical polymerization, the compositions comprising a mixture of a shock-sensitive peroxide and a diluent, the diluent being a monomeric material containing olefinic unsaturation which does not readily homopolymerize.

This application is a continuation-in--part of Application Serial No.758,282, filed Jan. 10, 1977, and now abandoned.

Many organic peroxides are known and used to initiate polymerization ofmonomers containing olefinical unsaturation. Many such peroxides areshock-sensitive and are handled usually only in diluted form. Generally,the addition of an appropriate diluent reduces the shock-sensitivity ofthe organic peroxide to the point where it can be safely handled. Theproblem of shock-sensitivity of such peroxides has been recognized formany years, for example, U.S. Patent 2,133,733 issued Oct. 18, 1938discloses the use of liquid hydrocarbons, preferably the hydrocarbonsboiling in excess of 100° C. in a quantity sufficient to wet theperoxide surface. U.S. Patent 3,538,011 discloses the use of variousplasticizers mixed with peroxides to reduce their shock-sensitivity.U.S. Patent 3,557,009 discloses the use of alcohols boiling between 130and 255° C. as a means of desensitizing peroxides. U.S. Patent 3,902,596discloses a catalyst package suitable for use in polyester systemswherein the catalyst is admixed with various oils or uncured polyesterresin and the peroxy-oil composition contained within a polystyrene filmenvelope. Oftentimes when peroxide compositions are employed in thefree-radical polymerization of olefinically unsaturated materials, thediluent material employed in the peroxide composition oftentimes has adeleterious effect on the polymer so-produced, for example, in thepolymerization of polystyrenes the presence of oils, hydrocarbondiluents, high molecular weight hydrocarbons and the like are notreadily removed from the polymer after polymerization and result in areduction in the heat-distortion temperature. With many thermoplasticpolymers, it is usually advantageous to maintain as high aheat-distortion temperature as possible, particularly when such polymersare employed for the manufacture of shaped articles such as by injectionmolding or thermoformed articles from extruded sheet.

It would also be desirable if there were available an improved methodfor the polymerization of olefinically unsaturated monomers employingorganic peroxide as a free-radical initiator.

It would also be desirable if there were available a polymerizationmethod using an improved organic peroxide composition of reducedshock-sensitivity which did not significantly reduce the heat-distortiontemperatures of polymers prepared therewith.

These benefits and other advantages in accordance with the presentinvention are achieved in an improvement in a method for polymerizingone or more olefinically unsaturated monomer, the method comprisingadmixing an organic peroxide with olefinically unsaturated polymerizablematerial maintaining the resultant mixture of monomeric material and afree-radical polymerization initiating peroxide at a polymerizingtemperature and converting at least a portion of the monomeric materialinto polymeric material, the improvement which comprises providing theorganic peroxide as an intimate admixture consisting essentially of (a)a shock-sensitive organic peroxide and (b) an olefinically unsaturatedmonomer, the olefinically unsaturated monomer which does nothomopolymerize, (a) being present in a proportion of 10 to 90 parts byweight and (b) being present in a proportion of 90 to 10 parts by weightper 100 parts by weight of (a) and (b).

Shock-sensitive organic peroxides which are handled in diluted form andare suitable for the practice of the present invention include:propionyl peroxide, acetyl peroxide, succinic acid peroxide, t-butylperoxyisobutylate, cyclohexanone peroxide, methyl ethyl ketone peroxide,2,2-bis-(t-butyl peroxy)butane, 1,1-bis(t-butyl peroxy)cyclohexane,t-butyl peroxy isopropyl carbonate,2,5-dimethyl-2.5-bis(benzoylperoxy)hexane, t-butylperacetate,t-butylperbenzoate, and di-t-butylperoxy phthalate.

By the term "reduced shock-sensitivity" is meant reduced E₅₀ value asdetermined by Liquid Propellant Information Agency Test No. 4,Drop-Weight Test, Joint Army-Navy-Air Force Panel on Liquid PropellantTest Methods, Silver Springs, Md., March 1960.

Monomers which exhibit no tendency to homopolymerize are those monomerswhich in admixture with an organic polymerization inducing peroxide suchas hereinbefore set forth do not polymerize to more than one percentconversion of monomer to polymer at 100 hours at 40° C. when the organicperoxide and monomer are present in a one-to-one ratio by weight.Typical non-homopolymerizing monomers include: maleic anhydride,dimethyl maleate, ethyl maleate, diethyl maleate, citriconic anhydride,dimethyl citriconate, methyl citriconate, ethyl citriconate,fumaronitrile, methyl fumurate, dimethyl fumurate, ethyl fumurate,diethyl fumurate, cinnamonitrile, methyl cinnamate, ethyl cinnamate,stilbene and the like.

Organic peroxy initiator compositons for the practice of the presentinvention are useful for initiation of polymerization of a wide varietyof monomers. Among the suitable ethylenically unsaturated monomers are:styrene, styrene with alkyl and halogen substituents on the ring andside chain such as o-, m- and p-methyl styrenes, alpha methyl styrene,2,4-dimethyl styrene, 2,3-dimethyl styrene, 2,5-dimethyl styrene, alphachlorostyrene, alpha ethyl styrene, p-ethylstyrene, m-propyl styrene,bromostyrene, dichlorostyrene, isopropenyl toluene, vinyl naphthalene,and the o-, m- and p-chlorostyrenes and bromostyrenes; esters ofalpha-methylene aliphatic monocarboxylic acids, such as methyl acrylate,ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate,2-chloroethyl acrylate, 2-chloropropyl acrylate, 2,2'-dichloroisopropylacrylate, phenyl acrylate, cyclohexyl acrylate, methylalpha-chloroacrylate, methyl methacrylate, ethyl methacrylate, methylethacrylate; acrylonitrile, methacrylonitrile; vinyl esters, such asvinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate,vinyl laurate, vinyl stearate, vinyl ethers such as vinyl methyl ether,vinyl isobutyl ether, vinyl 2-chloroethyl ether; vinyl ketones, such asvinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone;isobutylene; vinylidene halides, such as vinylidene chloride; vinylidenechlorofluoride; N-vinyl compounds such as N-vinyl pyrrole, N-vinylcarbazole, N-vinyl indole, N-vinyl succinimide; acrolein, methacrolein,acrylamide, methacrylamide, N-methylol acrylamide; and allyl compoundssuch as diallyl phthalate, tetrachlorodiallyl phthalate, allyl alcohol,methallyl alcohol, allyl acetate, allyl methacrylate, diallyl carbonate,allyl lactate, allyl alphahydroxyisobutyrate, allyl trichlorosilane,allyl acrylate, diallyl malonate, diallyl oxalate, diallyl gluconate,diallyl methylgluconate, diallyl adipate, diallyl sebacate, diallylcitraconate, the diallyl ester of muconic acid, diallyl itaconate,diallyl chlorophthalate, diallyl dichlorosilane, the diallyl ester ofendomethylene tetrahydrophthalic anhydride, triallyl tricarballylate,triallyl aconitate, triallyl citrate, triallyl cyanurate, triallylphosphate, trimethallyl phosphate, tetraallyl silane, tetraallylsilicate, hexallyl disiloxane, and the like. Unsaturated olefins such asethylene, propylene, butylene, hexene and exemplary monomers that can beemployed with the initiators useful for the invention are 1,3-butadiene;isoprene; piperylene; 2,3-dimethyll-1,3-butadiene; 1,3-octadiene;4,5diethyl-1,3-octadiene; styrene; 3-methylstyrene; 3,5-diethylstyrene;4-n-propylstyrene; 2,4,6,-trimethylstyrene; 3-methyl-5-n-hexylstyrene;2,3,4,5-tetramethylstyrene; 4-dodecylstyrene; 4-cyclohexylstyrene;4-phenylstyrene; 4-p-tolylstyrene; 1-vinylnaphthalene;2-vinylnaphthalene; 4-methyl-1-vinylnaphthalene; 3-ethyl-2-vinylnaphthalene; 4,5-dimethyl-1-vinylnaphthalene;4,5-diethyl-2-vinylnaphthalene; 6-isopropyl-1-vinylnaphthalene;2,4-diisopropyl-1-vinylnapthalene;4-n-propyl-5-n-butyl-2-vinylnaphthalene, and the like.

Polymerization of ethylenically unsaturated monomers employing theorganic peroxy compositions in accordance with the present invention maybe conducted in any of the conventional polymerization systems such asbulk, mass, mass suspension, solution, suspension and emulsionpolymerization. The compositions useful for the practice of the presentinvention are readily prepared by admixing the desired peroxide with thenon-homopolymerizable monomer. In cases where the monomer is liquid,such mix is readily accomplished at ambient or lower temperatures.Generally, it is desirable to add the peroxide to the monomer in thecase of a liquid mixture. When the monomer is a solid at ambienttemperature, generally it is desirable to pulverize the monomer to formthe plurality of particles. Beneficially such particles are sufficientlysmall to pass a 100-mesh US sieve size screen. If it is desired that theproportion of peroxide be substantially greater than about one-to-one,the monomer should be divided into particles having maximum surface.Frequently, in order to obtain monomer of high surface, it is oftendesirable to dissolve the monomer in appropriate solvent and precipitatethe monomer in a nonsolvent and recover the precipitate by filtering anddrying.

For purposes of comparison, four samples were prepared by polymerizingstyrene in a glass ampule at a temperature of 128° C. employing 0.4parts by weight of peroxy based on the weight of the styrene. Thepolymerizations were carried out to about 55-65 weight percentconversion of styrene to polystyrene. The ampules and contents were thencooled. The contents were removed and devolatilized at 210° C. for aperiod of one hour under a pressure of three millimeters of mercury.Four initiator systems (all nonshock-sensitive in accordance with LiquidPropellant Information Agency, Test No. 4, Drop-Weight Test) were used:one employed tertiarybutylperbenzoate admixed with silicone oil; asecond was tertiarybutylperbenzoate admixed with solid maleic anhydride;the third was 1,1-bis(t-butylperoxy)cyclohexane admixed with mineraloil, and the fourth was 1,1--bis(t-butylperoxy)cyclohexane admixed withdiethyl fumarate. In each case equal parts by weight of organic peroxideand diluent were employed. The devolatilized polymer was compressionmolded to provide a test specimen and the Vicat heat-distortiontemperature of the resultant polymer determined. Employingtertiarybutylperbenzoate as the catalyst, the sample containing siliconeoil had a distortion temperature of 225° F. while the sample employingmaleic anhydride in place of the silicone oil had a heat-distortiontemperature of 228° F. Samples employing the mineral oil anddiethylfumarate had a Vicat heat-distortion temperature of 224° F. and226° F. respectively. Although the foregoing illustrations show only theuse of a single organic peroxy compound, mixture of one or more of thehereinbefore delineated organic peroxy compounds with one or more of thehereinbefore delineated non-homopolymerizable monomers are readilyemployed. Such mixtures are particularly beneficial where it is desiredto conduct polymerization over an extended range of temperatures.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set fourth and defined in thehereto-appended claims.

What is claimed is:
 1. In a method for polymerizing one or moreolefinically unsaturated monomer, the method comprising admixing anorganic peroxide with olefinically unsaturated polymerizable materialmaintaining the resultant mixture of monomeric material and afree-radical polymerization initiating peroxide at a polymerizingtemperature and converting at least a portion of the monomeric materialinto polymeric material, the improvement which comprises providing theorganic peroxide as an intimate admixture consisting essentially of (a)a shock-sensitive organic peroxide and (b) an olefinically unsaturatedmonomer, the olefinically unsaturated monomer which does nothomopolymerize, (a) being present in a proportion of 10 to 90 parts byweight and (b) being present in a proportion of 90 to 10 parts by weightper 100 parts by weight of (a) and (b).
 2. The method of claim 1 whereinthe olefinically unsaturated monomer which exhibits no tendency tohomopolymerize is particulate.
 3. The method of claim 2 wherein theolefinically unsaturated monomer which exhibits no tendency tohomopolymerize has particles sufficiently small to pass a 100-mesh USsieve size screen.